In a wireless communication system, the battery capacity of a wireless communication device is limited as a result of device size. In order to conserve power, wireless communication devices often utilize discontinuous reception (DRX) techniques that allow the devices to power down certain circuitry when operating in an idle mode, commonly referred to as “sleep mode.” During DRX sleep mode, a wireless communication device typically disables a fast system clock and utilizes a lower-frequency clock for sleep counting. When the wireless communication device exits sleep mode, the fast system clock is restored using the sleep count.
The lower-frequency sleep clock in a wireless communication device is typically a 32 kHz clock source, provided by an external crystal oscillator. A crystal oscillator advantageously provides a relatively stable clock source, but may increase the cost and size of the integrated circuit.